#include <stdio.h>

double factorial(unsigned int i)
{
  if(i <= 1)
  {
    return 1;
  }  
  return i * factorial(i - 1);
}

int main(void)
{
   int i = 6;
   printf("%d 的阶乘为 %f\n",i,factorial(i));  
   return 0;
}
